80 DISINFECTANTS 



acting molecules should also apply to those of the dis- 

 infectants. As the latter are evidently not hindered at 

 all, and as the increased viscosity of protoplasm does 

 not influence appreciably the death rate, it does not seem 

 likely that it should influence the growth rate and there- 

 fore, it is probably not the cause of the cessation of life 

 functions at low temperatures. 



IV. INTERFERENCE OF FOREIGN MATTER WITH DISINFECTION 



Sterilization of water supplies and sterilization of in- 

 struments are perhaps the only cases where bacteria are 

 exposed to disinfectants in the absence of organic matter. 

 In most cases of disinfection, proteins are present, and 

 frequently other organic or inorganic substances. It is 

 important, therefore, to know to what extent foreign 

 matter interferes with sterilization. 



It has been stated before that probably all disinfec- 

 tants produce their killing effects by reacting with some 

 protein in the cell. They must be expected to react also 

 with proteins outside the cell. Obviously, disinfectants 

 will be weakened, or their action may even be com- 

 pletely nullified if they produce insoluble compounds 

 with foreign materials. Such is the case for silver ni- 

 trate in presence of chlorides, for mercury salts in pres- 

 ence of hydrogen sulfide, and for hydrogen peroxide in 

 open wounds, where it is decomposed by catalase. 



A particularly important instance is that of the disin- 

 fection of the living body in chemotherapy where the 

 compounds of the blood and of the tissues may tend to 

 combine with the toxic agent, thereby decreasing its con- 

 centration and efficiency. 



Different disinfectants will be affected differently by 

 the same foreign substance, and this is one of the 

 reasons why so many different kinds of disinfectants are 

 being used. 



